A common and efficient communication antenna used at a fixed location, includes a monopole radiating element, usually having a length of one-quarter wavelength, with a lower end lying at or slightly above the earth and with the antenna extending upwardly therefrom. The earthen ground plane provides the opposing element for the radiating system. Most AM broadcast stations use this approach. The monopole element may be elevated from the earth and ground and provided with an artificial, approximately horizontal ground plane formed by a conductive surface. Vehicle monopole radiators use this principle, by being mounted on or adjacent to a vehicle's metal roof or trunk surface, the metal surface providing an effective ground plane for the radiator.
Recently, vehicle bodies have been formed of composite plastic materials instead of metal, so there is no ground plane. A common solution is to connect an outer sheath of a coaxial feedline, to a metallic part of the frame such as the support structure, to provide at least some sort of opposing element. This is a marginal solution at best, due to the variables of poor conductivity, insufficient area, and movement of the connecting conductor. Marine applications have similar problems.